The immediate aims of this project are to identify those bacterial factors which are both necessary and sufficient for E. coli to colonize the mouse urinary tract in an ascending model of pyelonephritis. The investigators experiments to date indicate that P and type 1 fimbriae and the polysaccharide antigens O and K are necessary for E. coli to successfully colonize the mouse urinary tract. They now propose to determine which of these factors are sufficient for pathogenesis by transferring genes or gene clusters for these different traits singly and in combination into an E. coli K12 strain. The ability of these recombinants to resist serum killing and to colonize the urinary tract of mice will be assessed. The investigators also propose to further evaluate the biological characteristics of three different types of P-fimbriae by cloning the operons for each type of fimbria into a fecally-derived strain of E. coli that is otherwise nonpathogenic in the mouse model.